Abstract
Rice husk (RH) contains abundant silica such that RH silica (RHS) may be useful for possible industrial exploitation. Here, amorphous silica nanoparticles with multiple pore structures were acquired from RH by simple thermochemical processes. RHS antimicrobial activity and effects on zebrafish innate immunity against pathogen infections were evaluated. A toxicity assay showed that zebrafish exposed to an RHS dose lower than 200 μg/mL did not exhibit damage to zebrafish embryonic development or juvenile survival. RHS showed a wide spectrum of bacteriostatic activity against a variety of pathogens including antibiotic-resistant pathogens, implying its potential application as an antimicrobial agent in diverse industries. Fish exposed to 20 or 200 μg/mL RHS exhibited significantly increased mRNA expression of immune-related genes, including IL-1β, IL-6, IL-15, TNF-α, COX-2a, TLR-4a, lysozyme, and complement C3b. RHS-treated zebrafish exhibited a higher cumulative survival compared to that in control fish after infecting with Aeromonas hydrophila and Streptococcus iniae. The present results showed that a safe RHS dose enhanced innate immunity against infections without toxic effects in healthy fish, suggesting that RHS may be developed as an immunostimulant for improving health status in aquaculture.
Highlights
Aquaculture is considered the fastest growing food production industry in the world that is responsible for fish production to support the impressive increase in food demand for human consumption
ICP-MS analysis showed that the purity of SiO2 in the RH silica (RHS) was more than 98% but less than 99.0%
Embryos exposed to 2000 μg/mL RHS exhibited a significantly increased malformation rate, and the defects manifested as mainly pericardial edema, spinal curvature, yolk sac edema, and irregular muscle shape phenotypes
Summary
Aquaculture is considered the fastest growing food production industry in the world that is responsible for fish production to support the impressive increase in food demand for human consumption. Heavy use of antibiotics in aquaculture has caused impacts, including the emergence of antibiotic-resistant fish pathogens in aquatic environments, alterations of the bacterial flora in microbial ecology, reduced therapeutic efficacy of antibiotics, increased risk of food safety by residual antibiotic contamination, and increased horizontal transfer of antibiotic resistance genes to pathogens that pose risks to animals and human health [4]. Alternative strategies to antibiotics, such as vaccines [5], antimicrobial peptides [6], probiotics [7,8], natural extracts, and their bioactive compounds [9,10], have been developed as antimicrobials or immunostimulators for disease control in aquaculture. Some alternatives are workable for disease control in the laboratory, they are difficult to apply practically in aquaculture due to their high cost and lack of ease of use. Developing effective, inexpensive, and accessible antimicrobials or immunostimulators in aquaculture is a necessity
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